The present invention relates to a ceramic shell-and-tube type heat exchanger and a method for manufacturing the same.
Nowadays, the research and development of a forward type ceramic gas turbine have been carried out as a government project for the purposes of achieving high efficiency, low environmental pollution, the diversification of fuel, and the like. Thus, as one of factor devices of this ceramic gas turbine, a heat exchanger made of a ceramic material having an excellent performance as a heat-resistant material for high temperatures has been developed in place of conventional metallic materials. FIG. 11 shows a schematic side view illustrating a ceramic shell-and-tube type heat exchanger which has been heretofore developed. In this drawing, two tubular plates 1a, 1b are joined and fixed to both the end portions of a plurality of heat transfer tubes 2 which are tubular ceramics, and the above-mentioned two tubular plates 1a, 1b are plate-like ceramics having a plurality of through-holes into which these heat transfer tubes 2 are inserted to be fixed.
As a general method for preparing a ceramic shell-and-tube type heat exchanger, there is known a method which comprises: inserting the end portions of the heat transfer tubes which are the sintered tubular ceramics into throughholes of tubular plates 1 which are unsintered plate-like ceramics having the plurality of throughholes 3 as shown in FIG. 7, and then firing these members in this condition, thereby integrally joining both the members to each other by the utilization of a difference between firing shrinkage ratios of both the members (this joining technique utilizing the difference between the firing shrinkage ratios will be hereinafter referred to as "firing join").
That is, since the heat transfer tubes are already sintered, they hardly shrink during the firing process; while since the tubular plates are unsintered, the tubular plates have a higher shrinkage ratio than the heat transfer tubes. When firing is conducted under the aforementioned conditions, both ends of each heat transfer tube are tightened by a shrinkage of throughholes 3 in the tubular plates 1 according to the sintering, thereby unitarily joining the tubular plates 1 with the heat transfer tubes. An adequate interference of the firing join is determined in consideration of firing shrinkage ratios of the tubular plates and the heat transfer tubes, thereby providing more strong connecting conditions.
In this case, the firing can usually be carried out in such a condition as shown in FIG. 10 where in a sagger having a sealed structure for the purposes of preventing contamination with carbon and the like from furnace materials and of regulating an atmosphere, a setter 4 is placed, the heat transfer tubes 2 are stood on this setter 4 so as to be vertical to a floor surface, and the tubular plates 1a, 1b are positioned at both the upper and lower end portions of the tubes 2 by the use of jigs 5.
However, in the above-mentioned conventional manufacturing method, the heat transfer tubes tend to be deformed during the firing join step. Therefore, joining strength between the heat transfer tubes and the tubular plates tends to deteriorate, and gas leakage is inconveniently liable to occur owing to a joining failure between the heat transfer tubes and the tubular plates. When the heat transfer tubes are long, the heat transfer tubes are further noticeably deformed. Accordingly, it has particularly been difficult to manufacture the ceramic shell-and-tube type heat exchanger having the long heat transfer tubes.
As a means for controlling the deformation of the heat transfer tubes in a firing and joining process, the present inventor previously proposed that another tubular plate (middle tubular plate) 1c is placed between the two tubular plates 1a and 1c which were positioned at the upper and lower end portions of the heat transfer tubes as shown in FIG. 9 and that they are fired and joined simultaneously with supporting these tubular plates by a fixing jig 5 (U.S. patent application Ser. No. 08/411,261). Since, the heat transfer tubes 2 were bound in the middle portions by the middle tubular plate 1c in this method, it had a certain effect of controlling the deformations of the heat transfer tubes. However, it was not necessarily satisfied, and therefore, a more effective method was required.
Additionally, in a heat exchanger, it is the most important technical subject to improve its heat exchange efficiency. As one of the means, it is very effective to form fins on the heat transfer tubes, thereby enlarging a heat transfer area of the heat exchanger.
The present invention has been attained in view of such conventional circumstances. An object of the present invention is to provide a method for manufacturing a ceramic shell-and-tube type heat exchanger provided with fins, which can prevent the deformation of heat transfer tubes and simultaneously form fins of heat transfer tubes in a firing join step.